build(nix): drop rust-overlay

nixpkgs works well enough and gives us a good buffer in dealing with
compiler regressions

nix/containerize.nix

@@ -0,0 +1,9 @@
+{ lib, dockerTools }:
+refraction:
+
+dockerTools.buildLayeredImage {
+  name = "refraction";
+  tag = "latest-${refraction.passthru.dockerArchitecture}";
+  config.Cmd = [ (lib.getExe refraction) ];
+  architecture = refraction.passthru.dockerArchitecture;
+}

nix/static.nix

@@ -1,37 +1,9 @@
-{
-  lib,
-  refraction,
-  rust-overlay,
-  pkgsCross,
-}:
+{ pkgsCross }:
 let
   crossPlatformFor = with pkgsCross; {
     x86_64 = musl64.pkgsStatic;
     aarch64 = aarch64-multiplatform.pkgsStatic;
   };
-
-  toolchain = rust-overlay.rust.minimal.override {
-    extensions = [ "rust-std" ];
-    targets = lib.mapAttrsToList (_: pkgs: pkgs.stdenv.hostPlatform.rust.rustcTarget) crossPlatformFor;
-  };
-
-  rustPlatformFor = lib.mapAttrs (
-    _: pkgs:
-    pkgs.makeRustPlatform (
-      lib.genAttrs [
-        "cargo"
-        "rustc"
-      ] (_: toolchain)
-    )
-  ) crossPlatformFor;
 in
 { arch }:
-(refraction.override {
-  rustPlatform = rustPlatformFor.${arch};
-  optimizeSize = true;
-}).overrideAttrs
-  (old: {
-    passthru = old.passthru or { } // {
-      inherit toolchain;
-    };
-  })
+crossPlatformFor.${arch}.callPackage ./package.nix { optimizeSize = true; }